. How would you account for the following

How would you account for the following

(i) Frenkel defects are not found in alkali metal halides

(ii) Schottky defects lower the density of related solids

(iii) Impurity doped silicon is a semiconductor.

                                      OR

Explain the following properties giving suitable examples:

(i) Ferromagnetism

(ii) Paramagnetism

(iii) Ferrimagnetism